javascript - Node.js Promise 链未按所需顺序触发

Question

我创建了一个简单的 Promise 链示例。我的目标是触发以下 4 个函数以按顺序获得输出。即 1 2 3 4。

function WriteOne()
{
    return new Promise(function(resolve, reject)
    {
        console.log("1");
        resolve("true");
    })    
}

function WriteTwo()
{
    return new Promise(function(resolve, reject)
    {
        setTimeout(function(){console.log("2");}, 3000);
        resolve("true");
    })    
}

function WriteThree()
{
    return new Promise(function(resolve, reject)
    {
        setTimeout(function(){console.log("3");}, 1000);
        resolve("true");
    })
}

function WriteFour()
{
    return new Promise(function(resolve, reject)
    {
        console.log("4");
        resolve("true");
    }) 
}

WriteOne().then(WriteTwo).then(WriteThree).then(WriteFour);

当我执行它们时，它们按以下顺序触发:

1 4 3 2

我在这里做错了什么？

Answer 1

您需要在setTimeout回调中解决

function WriteOne() {
	return new Promise(function (resolve, reject) {
		console.log("1");
		resolve("true");
	});
}

function WriteTwo() {
	return new Promise(function (resolve, reject) {
		setTimeout(function () {
			console.log("2");
			resolve("true");
		}, 3000);
		
	});
}

function WriteThree() {
	return new Promise(function (resolve, reject) {
		setTimeout(function () {
			console.log("3");
			resolve("true");
		}, 1000);
		
	});
}

function WriteFour() {
	return new Promise(function (resolve, reject) {
		console.log("4");
		resolve("true");
	});
}

WriteOne().then(WriteTwo).then(WriteThree).then(WriteFour);